NASA SP-5022

TECHNOLOGY UTILIZATION REPORT

Technology Utilization Division

MICROPOWER LOGIC CIRCUITS

I

I From

LEWIS RESEARCH CENTER Cleveland, Ohio

Hard copy (HC) I Microfiche ( M F)

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

#

I I NASA SP-5022

Technology TECHNOLOGY Utilization UTILIZATION REPORT Division

I I MICROPOWER LOGIC I CIRCUITS

I By John C. Sturman I Lewis Research Center

Washington, D.C. May 1965

.

NOTICE

Th i s document w a s prepared under t h e spon- ~ s o r s h i p of t h e Nat iona l Aeronaut ics and Space Adminis t ra t ion . Nei ther t h e United S t a t e s Gov- ernment, no r NASA, nor any person a c t i n g on behalf of NASA :

A. Makes any warranty or r e p r e s e n t a t i o n , ex- pressed or impl ied , w i th r e s p e c t t o t h e accuracy , completeness , o r use fu lness of t h e informat ion contained i n t h i s document, or t h a t t h e u s e of any in fo rma t ion , a p p a r a t u s , method, or process d i s c l o s e d i n t h i s document may n o t i n f r i n g e privately-owned r i g h t s ; or

B. Assumes any l i a b i l i t i e s w i t h r e s p e c t t o t h e use o f , or f o r damages r e s u l t i n g from t h e use o f , any in fo rma t ion , appa ra tus , method, or process d i s c l o s e d i n t h i s document.

For sale by the Clearinghouse for Federal Scientific and Technical Information Springfield, Virginia 22151 - Price $0.75

f

FOREWORD

The Adminis t ra tor of t h e Nat ional Aeronaut ics and Space Adminis t ra t ion has ' e s t a b l i s h e d a Technology U t i l i z a t i o n Program f o r " the r ap id d isseminat ion of

informat ion . . . on t echno log ica l developments. . . which appear t o be u s e f u l f o r gene ra l i n d u s t r i a l a p p l i c a t i o n . " From a v a r i e t y of sou rces , such as NASA

and t h a t which has p o t e n t i a l i n d u s t r i a l u s e i s made g e n e r a l l y a v a i l a b l e . Thus American i n d u s t r y w i l l r e c e i v e informat ion from t h e n a t i o n ' s space program about t h e la tes t developments i n ope ra t ing techniques , management systems,

ous t e c h n i c a l f i e l d s .

1 Research Centers and NASA c o n t r a c t o r s , space- re la ted technology i s screened ,

, m a t e r i a l s , p rocesses , s t r u c t u r e s , and a n a l y t i c a l and des ign procedures i n numer-

This p u b l i c a t i o n i s p a r t of a s e r i e s designed t o provide t h i s t e c h n i c a l , in format ion . I t i s based on d a t a developed during a cont inuing series of i n -

I Center , Instrument and Computing Div i s ion , Jesse H. H a l l , Chief . house r e sea rch s t u d i e s of ultra-low-power c i r c u i t s by t h e Lewis Research

The r e p o r t was prepared by J. C. Sturman o f t h e Instrument SysLerns Research Branch, i n coord ina t ion with t h e Lewis Technology U t i l i z a t i o n Of f i ce .

The D i r e c t o r , Technology U t i l i z a t i o n Div i s ion Nat ional Aeronaut ics and Space Adminis t ra t ion

iii

LIST OF FIGURE3

Figure

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1 0

11

1 2

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Tab1 e

I

I1

Conventional T r a n s i s t o r I n v e r t e r C i r c u i t

Basic Complementary T r a n s i s t o r I n v e r t e r C i r c u i t

Reset -Se t F1 ip-F1 op

Compl ementary Toggle Flip-Flop

Power Drain f o r Rese t -Se t and Toggle F l ip-Flops

Basic S imi l a r -Trans i s to r I n v e r t e r

T r a n s i s t o r Input NOR

Simi la r -Trans i s to r Monostable Mul t iv ib ra to r

Welded Cordwood Logic Modules, Top V i e w

G a t e and Reset Fl ip-Flop Modules, S ide V i e w

Input Power as a Function of Frequency f o r D i f f e r e n t F1 ip-F1 op s

Single-Pulse Generator

Mult iple-Input Tr igger C i r c u i t

Dual-Voltage Power Supply

LIST OF TABLES

Fl ip-Flop Performance C h a r a c t e r i s t i c s

I n d u s t r i a l i z e d " C i r c u i t s Performance C h a r a c t e r i s t i c s I1

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CONTENTS

r NTRODUC TI ON

MICROPOWER LOGIC CIRCUITS

Descr ip t ion of B a s i c C i r c u i t s

Packaging of Uni t s

P o s s i b l e I n d u s t r i a l App l i ca t ions

OTHER INNOVATIONS I N RELATED CIRCUITRY

Single-Pulse Generator

Mu1 t i p l e - I n p u t T r igge r C i r c u i t

Dual-Voltage Power Supply

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V

INTRODUCTION

A number of d i g i t a l l o g i c c i r c u i t s t h a t were developed p r i m a r i l y t o f i l l a need f o r very low power l o g i c systems i n space-vehicles can be advantageously adapted for s p e c i f i c a p p l i c a t i o n s i n nonspace computer systems. The more prom- i s i n g c i r c u i t s were b u i l t and t e s t e d a t t h e NASA Lewis Research Center . A l - though c e r t a i n f e a t u r e s of t h e c i r c u i t s are considered t o be new developments, t hey are e s s e n t i a l l y based on o l d e r concepts t h a t have no t been widely app l i ed .

With r e l a t i v e l y simple engineer ing mod i f i ca t ions , a p p l i c a t i o n s of t h e s e c i r c u i t s , as w e l l as of t h r e e a n c i l l a r y c i r c u i t s descr ibed i n t h i s r e p o r t , w i l l be apparent f o r a v a r i e t y of c a p i t a l equipment and consumer products . These inc lude automated product ion systems, numerical ly c o n t r o l l e d machine t o o l s , measuring in s t rumen ta t ion , remote c o n t r o l s and alarm s y s t e m s , h i g h - f i d e l i t y r a d i o and recording s y s t e m s , and t e l e v i s i o n r e c e i v e r s .

MICROPOWER LOGIC CIRCUITS

Seve ra l mod i f i ca t ions of a d i g i t a l l o g i c c i r c u i t were designed for t h e lowest p o s s i b l e power consumption a t r e l a t i v e l y low ope ra t ing speeds. Although t h e b a s i c c i r c u i t s are p a r t i c u l a r l y s u i t e d t o t h e s e o p e r a t i n g c o n d i t i o n s , t hey can be adapted t o perform e q u a l l y as w e l l a t high power l e v e l s and speeds. These c i r c u i t s e x h i b i t many d e s i r a b l e f e a t u r e s , i nc lud ing n e a r l y i d e a l wave- forms and power t r a n s f e r e f f i c i e n c i e s t h a t are v i r t u a l l y independent of opera- t i n g c o n d i t i o n s w i t h i n t h e i r des ign range.

Desc r ip t ion of B a s i c C i r c u i t s

Most convent ional t r a n s i s t o r l o g i c c i r c u i t s can be de r ived from t h e s tand- a r d i n v e r t e r c i r c u i t shown i n f i g u r e 1. When a p o s i t i v e v o l t a g e i s app l i ed t o t h e i n p u t t e rmina l , c u r r e n t f lows through r e s i s t o r RB and t u r n s t h e t r a n s i s t o r on. switch or r e l a y c o n t a c t . In t h i s s ta te , the output i s clamped t o ground, no v o l t a g e i s supp l i ed t o t h e l o a d , and t h e power output i s zero. Power i s d i s s i - p a t e d , however, i n t h e c o l l e c t o r load r e s i s t o r %. waste of power, i t would be necessa ry t o make RC l a r g e .

I n t h e "on" or s a t u r a t e d s ta te , t h e t r a n s i s t o r ac t s much as a closed

I n o r d e r t o minimize t h i s

1

TOTAL LOAD 0 = w = RESISTANCE,

RL I\ I/

RB B n.fL

INPUT

- - Figure 1. - Conventional t r a n s i s t o r i n v e r t e r c i r c u i t .

I f t h e i n p u t were then connected t o ground, no c u r r e n t would flow i n t o t h e t r a n s i s t o r base and t h e t r a n s i s t o r would t u r n o f f . I n t h i s s ta te , t h e v o l t a g e a t t h e output i s determined by t h e r a t i o of % t o RL. For a l a r g e output v o l t - age, % must be r e l a t i v e l y small. This requirement i s i n d i r e c t oppos i t i on t o t h e condi t ion f o r minimum power l o s s i n t h e For a 50% du ty c y c l e , a maximum t h e o r e t i c a l power t r a n s f e r e f f i c i e n c y of 17.2% i s obtained when % i s made equal t o 0.707 RL.

I f on" s ta te .

I t i s c l e a r from t h e above t h a t t h e d i f f i c u l t y i n ob ta in ing maximum power t r a n s f e r e f f i c i e n c y over a c y c l e comprising t h e two states of the c i r c u i t i s be- cause of t h e c o n t r a d i c t o r y requirements f o r t h e va lues of t h e c o l l e c t o r load r e s i s t o r Q. t r a n s i s t o r t h a t a c t s as an open c i r c u i t when t h e f i r s t t r a n s i s t o r i s turned on and as a very low r e s i s t a n c e when i t i s turned o f f . The s imples t c i r c u i t of t h i s t y p e i s shown i n f i g u r e 2. which i s turned on by a nega t ive s i g n a l , as opposed t o the NPN t r a n s i s t o r Q1 which i s turned on by a p o s i t i v e s i g n a l . When a p o s i t i v e s i g n a l i s app l i ed t o t h e i n p u t , t r a n s i s t o r Q1 i s s a t u r a t e d and p u l l s t h e output t o ground whi le t h e same input c u t s o f f t h e t r a n s i s t o r Q2. S ince t h e t r a n s i s t o r Q2 now a c t s as an open c i r c u i t , no power i s drawn from t h e power supply. For a nega t ive or ze ro i n p u t , t he s ta tes are reversed; t h a t i s , t r a n s i s t o r Q2 i s s a t u r a t e d and de- l i v e r s nea r ly f u l l supply vo l t age t o t h e load . N o power i s l o s t i n t r a n s i s t o r

Q1. same way as f o r t h e convent ional i n v e r t e r ) i s 100%. I n p r a c t i c e , va lues above 90% are not d i f f i c u l t t o ob ta in .

This d i f f i c u l t y can be e l imina ted by r ep lac ing wi th a second

The added t r a n s i s t o r Q2 i s of t h e PNP type

The t h e o r e t i c a l power t r a n s f e r e f f i c i e n c y of t h i s c i r c u i t (computed i n t h e

+ vcc

INPUT

- Figure 2. - Basic complementary t r a n s i s t o r i n v e r t e r c i r c u i t .

2

+4.5v

Figure 3. - Reset-set f l i p - f l o p .

The b a s i c concept i l l u s t r a t e d can be extended t o provide a wide v a r i e t y of l o g i c c i r c u i t s using e i t h e r complementary (PNP and NPN) t r a n s i s t o r s or only one

' t ype of t r a n s i s t o r . The reset-set f l i p - f l o p shown i n f i g u r e 3 i s an example of one of t h e more complex c i r c u i t s b u i l t by combining two of t h e b a s i c complemen- t a r y i n v e r t e r s , I t s o p e r a t i o n can be compared wi th t h a t of a l a t c h i n g r e l a y , s i n c e e i t h e r t h e l e f t or t h e r i g h t h a l f can be turned on by a p p l i c a t i o n of a p u l s e t o t h e corresponding i n p u t t e rmina l . Figure 4 shows a similar f l i p - f l o p us ing s t e e r i n g d iodes t o make i t a t o g g l e or "divide-by-two" c i r c u i t . i c i r c u i t changes i t s conducting s i d e each time a p u l s e i s app l i ed t o t h e s i n g l e

' i n p u t . Performance c h a r a c t e r i s t i c s of t h e s e c i r c u i t s are p l o t t e d i n f i g u r e 5. Note t h a t i n t h e low k i l o c y c l e r eg ion f o r which they are designed t o o p e r a t e , each c i r c u i t consumes cons ide rab ly less than 100 microwatts. An i n d i c a t i o n of t h e ou tpu t c a p a b i l i t i e s of t h e s e c i r c u i t s i s given i n t a b l e I. A t 2,000 p u l s e s p e r second, t h e s e c i r c u i t s are capable of d e l i v e r i n g approximately 30 t i m e s t h e i r unloaded power d r a i n t o a u s e f u l load. A t h i g h e r f r e q u e n c i e s t h i s va lue f a l l s somewhat, but t h e t o g g l e f l i p - f l o p i s s t i l l 83% e f f i c i e n t a t 200 k i l o - c y c l e s and an i n p u t power of 3 m i l l i w a t t s . These c i r c u i t s are t h u s i d e a l as power d r i v e r s and as matching elements between low- and high-power systems.

This

3

+ 4.5v

OUTPUT

Figure 4 . - Complementary t o g g l e f l i p - f l o p .

UNLOADED POWER DRAIN PW

0 RESET S E T A TOGGLE

P I

r” l o 0 l I O 0 0 10.000 I00.000 0 I O 0

INPUT PULSE RATE, PPS

-0 OUTPUT

Q3

Figure 5. - Power d r a i n f o r reset-set and t o g g l e f l i p - f l o p s .

4

TABLE I.-FLIP-FLOP PERFORMANCE CHARACTERISTICS

Input Pulse power, rate

mW PP s

Pow e r Load e f f i -

r e s i s t or, ciency , k a %

--- -- 0.058 0 .06 2,000

1.8 2,000 10 and 1 0 96

0 . 1

--- --

1 . 9 20,000 10 and 10 94 25,000 --- --

(b) Toggle - supply vo l t age , 4.0 V

i

0.015 .022 .96

0 .5 3

0 2,000 2,000

200,000 200,000

5

The des ign of a second important group of c i r c u i t s i s based on t h e s imilar- t r a n s i s t o r i n v e r t e r c i r c u i t shown i n f i g u r e 6. This c i r c u i t u ses two t r a n s i s - t o r s of t h e same type t o provide many of t h e advantages of t h e complementary c i r c u i t s . ground p o t e n t i a l . _tor Q2, which i s thus turned o f f . t o ground through backward d iode D2 and t r a n s i s t o r Q ground. through R1 i n t o t h e base of t r a n s i s t o r Q2. on t o supply power t o t h e load . A two-input NOR gate based on t h i s concept i s shown i n f i g u r e 7. A s i g n a l p re sen t a t e i t h e r of t h e two i n p u t s w i l l cause t h e output t o drop t o zero .

When t r a n s i s t o r Q1 i s turned on, i t s c o l l e c t o r vo l t age drops t o near This drop i s coupled through d iode D1 t o t h e base of t r a n s i s -

Simultaneously, a conduction pa th i s provided t o clamp t h e output t o

When no inpu t i s app l i ed and t r a n s i s t o r Q1 %urns o f f , c u r r e n t f lows This c u r r e n t t u r n s t h e t r a n s i s t o r

F igure 6. - Basic s i m i l a r - t r a n s i s t o r i n v e r t e r .

HU-5 OUTPUT 0

33 pf

+ 1.2 v INPUT I 100K

100 K + A v r r +2 -2 v IN457

Figure 7 . - T r a n s i s t o r i n p u t NOR.

Another mod i f i ca t ion of t h e b a s i c c i r c u i t (shown i n f i g u r e 6) i s t h e mono- I s t a b l e m u l t i v i b r a t o r shown i n f i g u r e 8. This m u l t i v i b r a t o r i s b a s i c a l l y a

t iming c i r c u i t which on being t r i g g e r e d provides a pu l se of f i x e d width. The width of t h i s p u l s e can be va r i ed from a f e w microseconds t o many mi l l i s econds

, by proper choice of t h e t iming c a p a c i t o r CT. C i r c u i t s of t h e s e two types b u i l t a t t h e NASA Lewis Research Center ope ra t e a t power l e v e l s from a q u a r t e r of a microwatt t o many m i l l i w a t t s over t h e frequency range of a few k i l o c y c l e s t o more than a megacycle.

t 1.2v t2 .2v t 2 . 2 v t I .2v

100 K IOOK

OUTPUT0 OOUTPUT IN457 IN457

220K 200pf ,IC t1.2v OTRIGGER

I N PUT

CT A I/

I\

a

- -

Figure 8. - S i m i l a r - t r a n s i s t o r monostable m u l t i v i b r a t o r .

I t i s i n t e r e s t i n g t o cons ide r what can be accomplished wi th t h e use of 1 monostable m u l t i v i b r a t o r s . I f t h e r e a l i s t i c power consumptionvalue of 100

microwatts p e r u n i t i s assumed, i t would be p o s s i b l e t o bu i ld a computer con- t a i n i n g 15,000 such u n i t s t h a t would consume no more power than an o rd ina ry t h r e e - c e l l f l a s h l i g h t . A t p r e s e n t , t h e cost of such a s y s t e m would be pro- h i b i t i v e f o r i n d u s t r i a l a p p l i c a t i o n s . However, i f t h e power consumption i s in - creased by a t least 1 0 , u se fu l u n i t s can be b u i l t wi th low-cost components t h a t r e t a i n e s s e n t i a l l y a l l t h e advantages of t h i s t ype of c i r c u i t r y .

The advantages and d isadvantages of these c i r c u i t s may be compared wi th those of t h e c i r c u i t s more commonly used i n d i g i t a l a p p l i c a t i o n s . The most s i g n i f i c a n t advantage of t h e new c i r c u i t s i s , of course , t h e i r r e l a t i v e l y very low power consumption. I t i s t h i s lower power requirement t h a t g i v e s r ise t o a number of t h e o t h e r advantages of these c i r c u i t s . The saving of power i s due t o two s e p a r a t e e f f e c t s , both t h e r e s u l t of d r i v i n g t h e load from a t r a n s i s t o r

7

i n s t ead of a convent ional c o l l e c t o r load r e s i s t o r . E l imina t ion of t h e c o l l e c - t o r r e s i s t o r , without making any o t h e r changes i n t h e c i r c u i t , would save con- s i d e r a b l e power f o r t h e c o n d i t i o n of z e r o output vo l t age , because t h e lower t r a n s i s t o r (Q1 i n f i g u r e 2) sees a h igh impedance when i t i s turned on. I t t h e r e f o r e draws only a very s m a l l c u r r e n t . A f u r t h e r saving i n power i s r e a l i z e d by lowering t h e supply vo l t age . The l a t t e r saving r e s u l t s from t h e f a c t t h a t t h e output i s clamped t o t h e supply by t h e added t r a n s i s t o r , which e l imina te s t h e vo l t age drop a c r o s s a c o l l e c t o r r e s i s t o r , and a l lows t h e supply vo l t age t o be made equal t o t h e requi red output vo l tage . The h igh power out- put and e f f i c i e n c y a l s o al low one c i r c u i t of t h i s type t o d r i v e many more out- p u t s than can be d r iven by convent ional c i r c u i t s .

Another d i r e c t r e s u l t of t h e low i n t e r n a l power d i s s i p a t i o n and h igh e f f i c i e n c y i s a n e g l i g i b l e rise i n temperature . The component packing d e n s i t y can t h e r e f o r e be increased without t h e need f o r a u x i l i a r y cool ing means. S ince a decrease i n ope ra t ing temperature of l o o C approximately ha lves t h e f a i l u r e r a t e of components, t h e very small temperature r ise should r e s u l t i n i nc reased c i r c u i t r e l i a b i l i t y and ope ra t ing l i f e . The low power consumption of t h e s e c i r - c u i t s s i m p l i f i e s t h e requirements f o r standby power, which must be used i n t h e event of primary power l i n e f a i l u r e .

The r e l i a b i l i t y of c i r c u i t s of t h i s type i s a l s o due t o t h e i r h igh t o l e r a n c e t o r e l a t i v e l y l a r g e v a r i a t i o n s i n supply vo l t age and component c h a r a c t e r i s t i c s . Therefore , less expensive components can be used without adverse e f f e c t on c i r - c u i t r e l i a b i l i t y . A s an example, t h e two f l i p - f l o p c i r c u i t s con ta in ing o rd i - nary 10-percent carbon r e s i s t o r s ope ra t e r e l i a b l y over a temperature range of -20° t o + S O 0 C w i th in supply-vol tage l i m i t s of 3.5 t o more than 6 v o l t s .

The f a c t t h a t t h e output of t h e s e c i r c u i t s i s clamped t o e i t h e r t h e supply vo l t age o r t h e ground r e s u l t s i n a number of o t h e r advantages. A main advantage i s t h a t the output l e v e l s are very w e l l de f ined and d i f f e r by no more than a few t e n t h s of a v o l t from t h e clamping l e v e l , even under maximum load . Clamped ou tpu t s a l s o provide a low output impedance which, i n t u r n , i n h i b i t s unwanted response from l i n e t r a n s i e n t s and o t h e r no i se sou rces , and a l lows t h e output t o d r i v e loads re turned t o e i t h e r t h e supply vo l t age or t h e ground and thereby doubles the number of l oads t h a t t h e c i r c u i t can d r i v e .

F i n a l l y , s i n c e both pos i t ive-and negat ive-going ou tpu t s are a c t i v e l y d r i v e n by a t r a n s i s t o r , t h e l i m i t s normally imposed by RC t i m e c o n s t a n t s are e l imina ted and nea r ly i d e a l waveforms, wi th f a s t r ise and f a l l t i m e s , a re obta ined . A s an example, t h e reset-set f l i p - f l o p produces 50-nanosecond r ise and f a l l t i m e s when operated a t a power d r a i n of 50 microwatts .

The r e l a t i v e l y l a r g e number of components requi red i n t h e s e c i r c u i t s may be a major l i m i t a t i o n from t h e s t andpo in t of s i z e and c o s t . These c i r c u i t s may o f f e r s u f f i c i e n t advantages f o r v a r i o u s a p p l i c a t i o n s i n those i n s t a n c e s where t h e i r cos t can be j u s t i f i e d .

8

Packaging of Units

High packaging d e n s i t y and des ign f l e x i b i l i t y were d e s i r e d f o r aerospace

d i o d e s , were packaged i n i n d i v i d u a l modules, using t h e welded cordwood cons t ruc - t i o n shown i n f i g u r e 9 . The l a r g e s t module i s an e i g h t - s t a g e r i n g coun te r ; t h e smaller module below i t i s a g a t e c i r c u i t . A t t h e upper r i g h t i s t h e reset-set f l i p - f l o p , which has a l r e a d y been d i scussed . The s m a l l module below i t i s t h e t o g g l e f l i p - f l o p . I t i s of more r ecen t cons t ruc t ion , and al though i t has approximately as many components as t h e reset-set u n i t , i t i s on ly 56% as l a r g e . I t r e p r e s e n t s t h e h i g h e s t component d e n s i t y t h a t t h e NASA Lewis Research Center h a s achieved t o d a t e , namely, 130 components p e r cubic inch. F igu re 10 shows s i d e views of two of t h e s e modules.

I a p p l i c a t i o n s . Accordingly, t h e c i r c u i t s , containing s i l c o n t r a n s i s t o r s and

'

I

E IG H T - S TAG E RESET-SET FLIP-FLOP RING COUNTER

I

GATE TOGGLE MODULE FLIP -FLOP

Figure 9. - Welded cordwood l o g i c modules, t o p view.

F igu re 10. - G a t e and reset f l i p - f l o p modules, s i d e view.

9

With t h i s method of cons t ruc t ion , t h e 15,000-element computer, p rev ious ly mentioned t o g e t h e r w i th i t s power supply, could be b u i l t i n t o a s u i t c a s e . I t may soon be p r a c t i c a l t o bu i ld such c i r c u i t s i n i n t e g r a t e d form; when t h i s i s achieved, i t w i l l be p o s s i b l e t o package t h e computer i n a much smaller volume.

Poss ib l e I n d u s t r i a l Appl ica t ions

Two a d d i t i o n a l c i r c u i t s based on t h e ac t ive- load concept were cons t ruc t ed using t r a n s i s t o r s and d iodes of germanium i n s t e a d of t h e more c o s t l y s i l i c o n . One was a togg le f l i p - f l o p n e a r l y i d e n t i c a l i n c i r c u i t r y t o t h a t shown i n f i g u r e 4. t a b l e I I ( a ) . Note t h a t i t s o v e r a l l performance i s q u i t e s imilar t o t h a t of t h e low-power aerospace u n i t (wi th s i l i c o n t r a n s i s t o r s and d iodes c h a r a c t e r i z e d i n t a b l e I ( b ) ) , w i th t h e except ion t h a t a l l power l e v e l s have been increased by approximately an o r d e r of magnitude. However, as shown i n t a b l e I I ( a ) , t h e s tandby power l e v e l of 0 .5 m i l l i w a t t i s s t i l l f a r lower than t h a t r equ i r ed f o r any of t h e commercially a v a i l a b l e l o g i c c i r c u i t s .

The performance of t h i s " i n d u s t r i a l i z e d " c i r c u i t i s t abu la t ed i n

A more s t r i k i n g comparison of t h e d i f f e r e n t f l i p - f l o p des igns i s shown i n f i g u r e 11. The lower two curves ( a l s o graphed i n f i g u r e 5) are f o r t h e aero- space des igns (with s i l i c o n t r a n s i s t o r s and d iodes ) ; t h e middle curve i s f o r t h e " i n d u s t r i a l i z e d " complementary togg le f l i p - f l o p module wi th germanium s e m i - conductors; t h e upper curve i s f o r a convent iona l f l i p - f l o p module, which has c o l l e c t o r load r e s i s t o r s and i s designed t o ope ra t e a t t h e minimum power and speed comparable wi th those of t h e o t h e r c i r c u i t s . Note t h a t a l though t h e low- c o s t i n d u s t r i a l i z e d c i r c u i t does not ope ra t e wi th an inpu t power of less than s e v e r a l hundred microwatts , i t s power consumption i s only one-tenth t h a t of t h e conventional c i r c u i t . The convent ional c i r c u i t p rovides a maximum power output t o i t s load of 0.8 m i l l i w a t t a t a n e f f i c i e n c y of 13 t o 15%, compared wi th more than 8 m i l l i w a t t s f o r t h e i n d u s t r i a l i z e d c i r c u i t a t 80 t o 96% e f f i c i e n c y . Furthermore, t h e convent ional f l i p - f l o p c i r c u i t e x h i b i t s a v e r y poor waveform (shown i n f i g u r e l l ) , compared wi th i t s i n d u s t r i a l i z e d c o u n t e r p a r t , which p u t s ou t a p r a c t i c a l l y i d e a l waveform.

CONVENTIONAL TOGGLE

I c UNLOADED

POWER DRAIN mu

- - INDUSTRIALIZED" - -

-

- - MICROPOWER RESET-SET7

. I =--

- -

.01 too 1,000 10,000 100.000

FREQUENCY, PPS

Figure 11. - Input power as a f u n c t i o n of f requency f o r d i f f e r e n t f l i p - f l o p s .

10

TABLE 11.-"INDUSTRIALIZED" CIRCUITS PERFORMANCE CHARACTERISTICS

Input power mW

Power Pul se Load effi- rate resist or, ciency , PP s k f i %

0.5 12.5

11.7 10.9

.87

I 100 100

67,000 67,000 200,000

I

(b) Similar-transistor NOR gate - Total component cost per unit in quantities of 1000, $3.00; supply voltage, 6.0 V

0.755 4.63 .766 8.48 1.27 6.65

500 a 500 a

10,000 a 10,000 200,000 a 200,000

%ith 50% duty cycle. I

11

E s s e n t i a l l y , the same comments apply t o t h e performance of t h e th ree - inpu t s i m i l a r - t r a n s i s t o r NOR g a t e shown i n t a b l e I I ( b ) . A main f e a t u r e of t h e c i r - c u i t i s t h a t a l l semiconductor components, except the backward d iode , were of s i l i c o n t o ensure inc reased r e l i a b i l i t y and high-temperature ope ra t ion . The backward diode was of convent ional d e s i g n using germanium a t a cons ide rab le c o s t saving. The e f f i c i e n c y of t h i s c i r c u i t i s somewhat less than t h a t of the complementary c i r c u i t , as i s t o be expected, a l though i t i s apprec i ab ly above t h a t of t h e convent ional c i r c u i t s .

D i g i t a l systems g e n e r a l l y r e q u i r e some means of e n t e r i n g in fo rma t ion from i n p u t devices . A pushbutton or o t h e r mechanical c o n t a c t c l o s u r e i n conjunct ion wi th some type of network i s commonly used t o provide a s i n g l e p u l s e t o perform the required f u n c t i o n . F a s t - r i s e s i n g l e p u l s e s cannot be r e l i a b l y ob ta ined

cons t an t f i l t e r s and magnetic t r i g g e r c i r c u i t s reduce c o n t a c t bounce problems cons ide rab ly , bu t have r a t h e r l i m i t e d f l e x i b i l i t y for providing p u l s e s of fas t - r ise time and widely v a r i a b l e width.

, wi th such c o n t a c t s , however, because of t he i r tendency t o bounce. Long t i m e -

These problems can be solved by t h e r a t h e r s imple c i r c u i t shown i n f i g u r e 12 . The c i r c u i t employs e i ther a T h y r i s t o r or an SCR ( s i l i c o n c o n t r o l l e d rect i - f i e r ) as t h e a c t i v e element. I t makes use of t h e c h a r a c t e r i s t i c t h a t once the element i s i n the conducting s t a t e , t h e supply v o l t a g e must be switched o f f t o r e t u r n the element t o t h e nonconducting state.

With t h e i n p u t switch or r e l a y i n t h e p o s i t i o n shown, t h e SCR w i l l n o t con- d u c t , because there i s no c u r r e n t sou rce t o the g a t e i n p u t . Cur ren t w i l l f low through R 1 and t h e switch c o n t a c t , charging t h e c a p a c i t o r .

12

~

These two c i r c u i t s ( t h e i n d u s t r i a l i z e d complementary f l i p - f l o p and the s i m i l a r - t r a n s i s t o r NOR g a t e ) , a l though n o t optimized f o r c o s t or performance, f u r t h e r i n d i c a t e some of t h e advantages t o be gained from t h e use of t h e s e c i r - c u i t concepts. V a r i a t i o n s of these c i r c u i t s can e a s i l y be designed. For example, the a v a i l a b i l i t y of h i g h - q u a l i t y , inexpensive s i l i c o n NPN t r a n s i s t o r s would recommend t h e i r use w i t h germanium PNP t r a n s i s t o r s i n complementary c i r - c u i t s . A hybrid l o g i c system wi th complementary- t ransis tor m u l t i v i b r a t o r s and s i m i l a r - t r a n s i s t o r g a t e s could very w e l l be economically competi t ive w i t h con- ven t iona l c i r c u i t s .

OTHER INNOVATIONS I N RELATED CIRCUITRY

Several o t h e r u s e f u l d i g i t a l l o g i c c i r c u i t s have been developed by the NASA L e w i s Research Center and i t s c o n t r a c t o r s . Although t h e s e c i r c u i t s were designed t o s o l v e s p e c i f i c problems, t h e i r a p p l i c a b i l i t y i s of much broader scope.

Single-Pulse Generator

r L ALTERNATE POSITION OF LOAD RESISTOR R2 FOR :: - REVERSED POLARITY f--- - 4 ALTERNATE OUTPUT

E=t lOv I _ C T 0.06pf

2N1872

R2 OUTPUT 100

IOK 0 PUL,,

I K

RISE TIME, 0.2psec k PULSE WIDTH,Gpsec cc

Figure 12. - Single-pulse g e n e r a t o r .

When t h e switch i s closed t o t h e g a t e i n p u t , s u f f i c i e n t c u r r e n t f lows through R1 t o cause conduction. The c a p a c i t o r , t h e r e f o r e , q u i c k l y d i s c h a r g e s through R2 and produces t h e output p u l s e with a peak amplitude equal t o E and a width equal t o R2C. Once t h e c a p a c i t o r i s d i scha rged , t h e SCR s t o p s conducting. The switch used must be of a nonbridging type , so t h a t when i t i s r e tu rned t o i t s o r i g i n a l p o s i t i o n , t h e g a t e c u r r e n t i s removed be fo re r e t u r n of t h e anode supply vo l t age .

If p u l s e s of t h e oppos i t e p o l a r i t y are d e s i r e d , i t i s necessa ry only t o move t h e load r e s i s t o r R2 t o t h e anode c i r c u i t as shown by t h e dashed r e s i s t o r i n t h e f i g u r e . A l t e r n a t i v e l y , a p u l s e t ransformer can be used i n con junc t ion w i t h t h e load r e s i s t o r t o provide an ou tpu t of e i t h e r p o l a r i t y as w e l l as a f l o a t i n g or m u l t i p l e output . The t ransformer must be terminated t o p re se rve waveshape, and i t s t i m e cons t an t must be wi th in t h e range of t h e r equ i r ed p u l s e widths .

Mult iple-Input Trigger C i r c u i t

I n o r d e r t o d e t e c t when a dc vo l t age exceeds a g iven l e v e l , some form of t r i g g e r or comparator c i r c u i t i s r equ i r ed . The usua l procedure i s t o have a s e p a r a t e t r i g g e r f o r each i n p u t , even i f i t i s necessa ry only t o d e t e c t wnen any one of t h e i n p u t s has exceeded a p a r t i c u l a r set p o i n t . The c i r c u i t of f i g u r e 13 e l i m i n a t e s d u p l i c a t i o n of t r i g g e r c i r c u i t s and a s s o c i a t e d l o g i c c i r - c u i t s by providing a means of coupling a number of i n p u t s t o one t r i g g e r (a Schmitt t r i g g e r c i r c u i t ) wh i l e maintaining c o n t r o l of each set p o i n t . Each of t h e t h r e e i n p u t s ( A , B, and C) i s e l e c t r i c a l l y p o s i t i v e , and t h e inpu t te rmina ls are connected through a po ten t iome te r t o a negat ive vo l t age . The v a r i a b l e con- t ac t on t h e po ten t iome te r i s connected through a low-leakage diode t o t h e i n p u t of t h e Schmit t t r i g g e r . Each potent iometer i s set so t h a t t h e vo l t age appearing a t i t s v a r i a b l e c o n t a c t w i l l j u s t become p o s i t i v e when t h e i n p u t l e v e l reaches t h e d e s i r e d t r i p p o i n t . This p o s i t i v e vo l t age w i l l cause c u r r e n t t o flow through t h e d iode and t r i p t h e t r i g g e r c i r c u i t t o change i t s output vo l t age .

There i s no coupl ing between i n p u t s ; each inpu t w i l l , t h e r e f o r e , t r i g g e r t h e c i r c u i t independent ly a t i t s p a r t i c u l a r t h re sho ld r e g a r d l e s s of t h e s i g n a l appl ied t o t h e o t h e r i n p u t s -- provided, of course , t h a t t h e c i r c u i t has no t y e t been t r i g g e r e d . This c i r c u i t should provide cons ide rab le sav ings i n alarm sys t ems i n which a number of v a r i a b l e s such as p r e s s u r e , t empera ture , neut ron f l u x , and such need t o be monitored s imultaneously.

I

Dual-Voltage Power Supply

L

I t i s commonly necessary t o supply s e v e r a l d i f f e r e n t v o l t a g e s t o e l e c t r o n i c These vo l t ages may be obtained from s e p a r a t e power s u p p l i e s or from

If vo l t age r e g u l a t i o n equipment. vo l t age - regu la t ing dev ices connected t o one main supply. i s no t r equ i r ed , t h e use of v o l t a g e r e g u l a t o r s f o r supplying power adds add i t ion - a l complexity and expense.

A simple s o l u t i o n i s provided by t h e c i r c u i t of f i g u r e 14 . The p o r t i o n of t h e c i r c u i t comprising d iodes D1 and D2, choke L , and c a p a c i t o r C 1 c o n s t i t u t e s a convent ional choke inpu t power supply. Choke inpu t s u p p l i e s have t h e cha rac t e r - i s t i c of providing an output vo l t age t h a t i s somewhat less than t h e r m s vo l t age appearing a c r o s s one h a l f of t h e t ransformer secondary.

The vo l t age a t po in t A i s ful l -wave r e c t i f i e d and has a peak ampli tude of n e a r l y 1 .4 V r m s . r e l a t i v e l y n e g l i g i b l e , so t h a t t h e h igh vo l t age a t t h e output i s very n e a r l y 1 . 4 V rms. c i r c u i t elements ( a d iode and a c a p a c i t o r ) are used.

The vo l t age drops a c r o s s semiconductor d iodes D1 and D 3 are

The output i s full-wave r e c t i f i e d , even though only two a d d i t i o n a l

The advantages of t h i s c i r c u i t are i t s s i m p l i c i t y ; t h e f a c t t h a t i t does no t use a s p e c i a l t ransformer ; and t h e f a c t t h a t i t s e f f i c i e n c y i s h igh , s i n c e no power i s l o s t i n voltage-dropping elements . The h igh-vol tage output can approach 1 . 5 t i m e s t h e low-voltage ou tpu t , and t h e r a t i o may be modified by proper choice of components. ins t ruments a s w e l l as r a d i o and t e l e v i s i o n s y s t e m s .

This c i r c u i t should f i n d use i n many i n d u s t r i a l

INPdT

14

Figure 13. - Mult ip le - input t r i g g e r c i r c u i t .

)LTAGE

VOLTAGE _ . . - .

-

Figure 14. - Dual-voltage power supply.